Effect of preheating-induced structural changes of mung bean starch and protein on the phase behavior, physicochemical properties, and digestibility of composite hydrogels

Abstract

Mung bean starch (MBS) and mung bean protein (MBP) were preheated at different moisture contents (20–80 %) to create biopolymers with different characteristics. For MBS, preheating led to different degrees of gelatinization, whereas for MBP it led to different degrees of protein aggregation and surface hydrophobicity. Pre-gelatinized starch formed junctions with double helix structures arranged in the amorphous region and the particle size increased. As the degrees of gelatinization of starch increased, the composite hydrogels changed their structure from having a starch-rich continuous phase, to a bicontinuous network, to having a protein-rich continuous phase. Moreover, the mechanical strength and water holding properties of the composite hydrogels decreased and their starch digestibility increased. This effect was mainly attributed to the disruption of the starch structure and the formation of a more open gel network, which facilitated the ability of the amylases to hydrolyze the starch molecules. Preheating the protein did not have as large an impact on the microstructure of the composite hydrogels as the starch. However, the presence of the MBPs with higher surface hydrophobicity prompted its interaction with starch, resulting in a significantly softer gel with slower digestion, which was attributed to their stronger ability to interfere with crosslinking between the starch molecules. Correlation and principal component analysis indicated starch and protein structures had significant internal correlations. Starch structure dominated, while protein structure modulated gel properties. Preheating-induced structural changes in starch and protein enhance composite gel diversity.